Methods, systems, and apparatus, for an infrared detector are provided. In one aspect, an infrared detector is provided that includes a pyroelectric sensor a controller for receiving a trigger signal outputted by the pyroelectric sensor a thermopile sensor, wherein the controller starts the thermopile sensor after receiving the trigger signal output by the pyroelectric sensor and an alarm, wherein the controller controls the alarm to generate an alarm signal in response to a determination that a difference between a current temperature and a background temperature detected by the thermopile sensor is larger than a threshold value and a determination that the areas of the thermopile sensor activated correspond to a human being.
